Sheet stacking apparatus

Abstract

In a sheet stacking apparatus, a sheet stacking unit stacks sheets conveyed by a sheet conveyance device. Three sheet extraction portions allow to selectively extract the sheets stacked on the sheet stacking unit from one of three directions including the downstream side of the sheet conveyance direction and two directions perpendicular to the sheet conveyance direction. A plurality of first detection sensors are provided in at least two of the three sheet extraction portions to detect an object that enters the sheet stacking unit. A second detection sensor detects the moving direction of the sheets stacked on the sheet stacking unit. A control device stops the operation of the sheet conveyance device when the first detection sensor detects the object, and disables the detection operation of the first detection sensor corresponding to the moving direction of the sheets when the second detection sensor detects the moving direction of the sheets.

1. A sheet stacking apparatus comprising:
 a sheet stacking unit which stacks sheets conveyed by a sheet conveyance device; 
 three sheet extraction portions which allow to selectively extract the sheets stacked on said sheet stacking unit from one of three directions including a downstream side of a sheet conveyance direction and two directions perpendicular to the sheet conveyance direction; 
 a plurality of first detection sensors which are provided in at least two of said three sheet extraction portions to detect an object that enters said sheet stacking unit; 
 a second detection sensor which detects a moving direction of the sheets stacked on said sheet stacking unit; and 
 a control device which stops an operation of the sheet conveyance device when at least one of said plurality of first detection sensors detects the object, and disables a detection operation of at least one of said first detection sensors corresponding to the moving direction of the sheets when said second detection sensor detects the moving direction of the sheets. 
 
     
     
       2. An apparatus according to  claim 1 , wherein said first detection sensors are provided in all of said three sheet extraction portions. 
     
     
       3. An apparatus according to  claim 1 , wherein said second detection sensor is provided on an upstream side of the sheet conveyance direction of said sheet stacking unit. 
     
     
       4. An apparatus according to  claim 1 , wherein said second detection sensor includes a pair of distance sensors which are arranged at a predetermined interval in a direction perpendicular to the sheet conveyance direction. 
     
     
       5. An apparatus according to  claim 4 , wherein when said pair of distance sensors detect the sheet and then one of said pair of distance sensors detects the sheets no longer, movement of the sheets in the direction perpendicular to the sheet conveyance direction is detected. 
     
     
       6. An apparatus according to  claim 4 , wherein when one of said pair of distance sensors detects a predetermined moving amount of the sheets in the direct perpendicular to the sheet conveyance direction, movement of the sheets in the direction perpendicular to the sheet conveyance direction is detected. 
     
     
       7. An apparatus according to  claim 4 , wherein when both of said pair of distance sensors detect movement of the sheets to a predetermined position on the downstream side of the sheet conveyance direction, movement of the sheets to the downstream side of the sheet conveyance direction is detected. 
     
     
       8. An apparatus according to  claim 4 , wherein when both of said pair of distance sensors detect separation from the sheets by not less than a predetermined distance on the downstream side of the sheet conveyance direction, movement of the sheets to the downstream side of the sheet conveyance direction is detected. 
     
     
       9. An apparatus according to  claim 4 , wherein said pair of distance sensors are arranged at an interval smaller than a widthwise length of a sheet of minimum size. 
     
     
       10. An apparatus according to  claim 4 , wherein said pair of distance sensors are oriented toward the downstream side of the sheet conveyance direction in a direction parallel to the sheet conveyance direction. 
     
     
       11. An apparatus according to  claim 4 , wherein said pair of distance sensors are arranged toward the downstream side of the sheet conveyance direction while being tilted in directions opposite to each other at the same angle.